On Wed, Nov 17, 2010 at 12:23 PM, dexen deVries <dexen.devr...@gmail.com> wrote: > On Wednesday 17 November 2010 18:14:35 Venkatesh Srinivas wrote: >> (...) >> I'd be very careful with vac -m and -a on Unix; both have been at the >> root of considerable data-loss on a unix venti for me. I'd recommend >> vac-ing tarballs, rather than using vac's on unix trees directly. But >> your mileage may vary... > > > could you please elaborate a bit about that data loss? > traversing symlinks breaks? some files not getting read by vac at all?
I have a number of vac archives that were made by vac-ing my homedir that cannot be mounted (venti can't find some of the scores in the tree). However, they did pass scrubbing (scrub was a tool i wrote that is sorta like half of venti/copy -- it traverses a tree, checks hashes, but doesn't write them out to anything). I have a number of trees in which somehow the SHA1 of the empty string was inserted: 'da39a3ee...'. And I have a number of trees that were venti/copied from one venti to another but somehow damaged (scores missing) after the copy, without seeing errors. vac -a in particular was good at producing archives which either don't mount or are filled with missing scores or zero-scores vs sha1(empty string) problems. Unvac is not useful for anything involving directories, since it outputs dirs which cannot be modified. http://groups.google.com/group/plan9port-dev/browse_thread/thread/8b0e2bc4b45d12b0 is a reasonably common bug from vac, seen on deep-ish directory trees. Two threads i can't find on the google groups interface, from p9p-dev as well: 1) 8/12/09 'venti/vac/vacfs trouble' and 2) 8/17/09 'vac errors'. Both bugs still exist afaik. I've seen this: cache block 501: type 8 score <lots of zeros>1f6 iostate 1 addr 502 ref 0 nlock 1 cache block 502: type 8 score <lots of zeros>1f7 iostate 1 addr 503 ref 0 nlock 1 cache block 503: type 8 score <lots of zeros>1f8 iostate 1 addr 504 ref 0 nlock 1 (output starts at 0x000...000 ;; goes up to score 0x000...200). vtcachebumpblock: no free blocks in vtCachezsh: IOT instruction ./vac -s -v -h tcp!acm.jhu.edu!17034 /export/home happen on deep-ish directory trees as well; I never managaed to track it down, though. Most recently, I've run two venti servers; vac targets the first one, every night the score is venti/copied to the second server. After two weeks, the two servers (with identical initial configuration) had different size and block counts from the http://.../storage. -- vs
